Numerical Investigation on Residual Stresses of the Safe-End/Nozzle Dissimilar Metal Welded Joint in CAP1400 Nuclear Power Plants

doi:10.1007/s40195-018-0803-8

Abstract

Abstract:

The residual stress evolution in a safe-end/nozzle dissimilar metal welded joint of CAP1400 nuclear power plants was investigated in the manufacturing process by finite element simulation. A finite element model, including cladding, buttering, post-weld heat treatment (PWHT) and dissimilar metal multi-pass welding, is developed based on SYSWELD software to investigate the evolution of residual stress in the aforementioned manufacturing process. The results reveal a large tensile axial residual stress, which exists at the weld zone on the inner surface, leads to a high sensitivity to stress corrosion cracking (SCC). PWHT process before dissimilar metal multi-pass welding process has a great influence on the magnitude and distribution of final axial residual stress. The risk of SCC on the inner surface of the pipe will increase if PWHT process is not taken into account. Therefore, such crucial thermal manufacturing process such as cladding, buttering and post-weld heat treatment, besides the multi-pass welding process, should be considered in the numerical model in order to accurately predict the distribution and the magnitude of the residual stress.

Key words: CAP1400 nuclear power plants, Nozzle, Safe-end, Dissimilar metal welding, Residual stress

Wen-Chao Dong, Dian-Bao Gao, Shan-Ping Lu. Numerical Investigation on Residual Stresses of the Safe-End/Nozzle Dissimilar Metal Welded Joint in CAP1400 Nuclear Power Plants[J]. Acta Metallurgica Sinica (English Letters), 2019, 32(5): 618-628.

Figures/Tables 18

Table 1 Welding process parameters

Welding procedure	Welding method	Current (A)	Voltage (V)	Welding speed (mm/min)
Cladding	GTAW	120-180	10-16	140-220
Cladding		120-170	10-12	160-240
Buttering		120-160	10-12	110-180
Welding		120-160	10-12	110-180

Fig. 1 Schematic of measured position for welding thermal cycle curve and residual stress

Fig. 2 Dimension and finite element model for CAP1400 nozzle/safe-end welded joint

Fig. 3 Schematic of double ellipsoid heat source model

Fig. 4 Thermodynamic properties for nuclear materials: a ER308L, b 316L steel, c Inconel 52 M, d SA508III steel

Table 2 Values of A and n from Ref. [7]

Material used in this work	Material used in Ref [7]	A	n
SA508 Gr.3	SA533B-1	2.82 × 10^-17	5.24
ER308L	Type 309L SS	1.49 × 10^-28	9.88
Inconel 52M	Alloy 82	1.68 × 10^-22	6.11

Fig. 5 Comparisons of the experimental and the calculated results of weld cross-section morphology and size

Fig. 6 Comparisons of welding thermal cycle curves between experiment and simulation for TC1, TC2 and TC3 points

Table 3 Fitting parameters for double ellipsoid heat source model

Q_f (W/mm³)	Q_r (W/mm³)	a_f (mm)	a_r (mm)	b (mm)	c (mm)	Q (W)
25	30	3	4	3	1.5	1100

Fig. 7 Finite element model for a bead-on-plate welding

Fig. 8 Contours of residual stress distribution: a longitudinal, b transverse (unit: MPa)

Fig. 9 Comparison of simulation results and measurements of residual stress profiles on the plate surface: a longitudinal, b transverse

Fig. 10 Schematic diagram for different paths

Fig. 11 Axial a, hoop b residual stress distributions on the inner surface during the manufacturing processes

Fig. 12 Through-thickness variations of axial and hoop residual stresses after dissimilar metal multi-pass welding a along Path 1 and b along Path 2

Fig. 13 Variations of axial and hoop residual stresses after dissimilar metal multi-pass welding on the outer surface

Fig. 14 Axial residual stress contours of Case A, Case B

Fig. 15 Hoop residual stress contours of Case A, Case B

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